Apparatus for twisting strands



Sept. 4, 1962 G. E. HENNING APPARATUS FOR TWISTING STRANDS 2 Sheets-Sheet 2 Filed Nov. 10, 1958 n mk o INVENTOR c. E. HE/VN/NG A I'TORNEI/ 3,5Z,0?9 Fatented Sept. 4, 1962 3,052,079 APPARATUS FOR TWISTING STRANDS George E. Henning, Baltimore, Md, assignor to Western Electric Company, Incorporated, New York, Nil, a corporation of New York Filed Nov. 10, 1958, er. No. 772,875 6 Qlairns. ttCi. 57-34) The present invention relates generally to apparatus for twisting strands, and more particularly to apparatus for imparting an alternating succession of twists to a plurality of advancing parallel strands.

In the manufacture of cables for use in the telephone industry, it is usually necessary to intertwist a pair of individually insulated wires to form a twisted pair. A plurality of the twisted pairs are then fed into a strander, wherein the twisted pairs are associated together into stranded units. In the past, it has been customary to twist the individually insulated wires together into a twisted pair in an operation distinct from the stranding operation. In such twisting operations, either the strand supply or the take-up was rotated about the axis of the wires in order to impart a unidirectional twist to the Wires.

it is now proposed to impart an alternating succession of twists to successive portions of an advancing pair of Wires in order to enable twisting without rotating either the supply or the take-up about the axis of the wires. This procedure enables the twisting and stranding operations to be performed in tandem, without an intermediate takeup or supply.

An object, therefore, of the present invention is to provide new and improved apparatus for twisting strands.

Another object of the invention is to provide apparatus for imparting an alternating succession of twists to a pin rality of advancing strands.

Still another object of the invention is to provide apparatus for imparting an alternating succession of twists to a pair of advancing parallel wires.

An apparatus for intertwisting a plurality of advancing strands, illustrating certain features of the invention, may include means for gripping the advancing strands against twisting at spaced points therealong, means for advancing the gripping means with the strands, and means for intertwisting the strands in the spans extending between the gripping means during the advancement of the gripping means with the strands.

Preferably, three aligned gripping members, such as pulleys about the peripheries of which the strands pass or nip rollers between which the strands pass, are mounted on a reciprocating carriage and means are provided for reciprocating the carriage so that the gripping members alternately advance with and return against the advancing strands. Means are provided for rotating the central gripping member about the line of advancement of the strands during at least a portion of the forward stroke of the carriage to impart twists of opposite hands to the strand lengths extending between the central gripping member and the end gripping members on either side thereof. During the return stroke of the carriage, the twisting rotation of the central gripping member is stopped to allow the twisted portion of the strands to pass out of engagement with the twisting members.

Other objects and advantages of the invention will appear from the following detailed description of specific embodiments thereof, when read in conjunction with the appended drawings, in which:

\FIG. 1 is an elevational View of a pair of wires intertwisted in accordance with the invention;

FIG. 2 is a schematic elevational view showing an apparatus for producing a stranded cable core, which apparatus includes a twisting unit according to the invention;

FIG. 3 is a schematic illustration of certain methods for twisting a pair of wires and is composed of FIGS. 3-A, 3B and 3-C, each of which depicts a step in one complete cycle of operation;

FIG. 4 is a front elevation of a twisting unit illustrating the principles of the invention;

FIG. 5 is an enlarged vertical sectional view of the twisting unit, taken generally along the line 55 of FIG. 4 in the direction of the arrows;

FIG. 6 is a schematic diagram of an electrical control circuit for operating the apparatus of FIGS. 4 and 5 in accordance with the principles of the invention, and

HG. 7 is a fragmentary View, similar to FIG. 4 and illustratin an alternative embodiment of the invention.

Referring now in detail ot the drawings, and in particular to FIG. 1, there is shown portions of a twisted pair, designated generally by the numeral 10, of individual wires 11 and 12, such as polyethylene-insulated copper wires, having an alternating succession of twists imparted thereto according to the principles of this invention. It will be observed that the portion of the twisted pair 10 extending to the left of a point A is provided with a right-hand twist and the portion extending to the right of point A is provided with a left-hand twist, the point A designating the transition point between the right-hand twisted section and the left-hand twisted section.

When the wires 11 and 12 comprise the polyethyleneinsulated copper Wires normally encountered in the telephone industry, there is substantially no tendency for the opposing twists extent on either side of the point A to cancel each other, due to the inherent properties of such wires. It should be understood, however, that in the event it is desired to impart an alternating succession of twists to a relatively resilient strand, the twisted strands may be taped, wrapped, or otherwise secured to prevent cancellation of the opposing twists.

Referring now to FIG. 2, illustrating schematically a complete apparatus utilizing the type of twisted pair 10 illustrated in FIG. 1, a plurality of bare copper wires 13-13 may be continuously withdrawn from supply reels 14 14 by a capstan 16 of any suitable type and advanced through a series of extruders 17-17, which apply polyethylene insulation about the bare wires 13-13 to form the individually insulated wires 11-41 and 1212 to be twisted together according-to the principles of this invention. The insulated wires 11-1-1 and 12-12 advance in pairs into a number of twisting units, designated generally by the numerals 18-18, and are twisted into pairs 1010, as illustrated in FIG. 1. The twisted pairs 10-10 then advance to a conventional strander, designated generally by the numeral 19, wherein they are associated together into a stranded unit 21 which then passes around the capstan 16 to a take-up reel 22.

Referring now to FIG. 3, illustrating generally the twisting methods, a pair of wires 11 and 12 to be twisted advance from right to left in closely spaced, parallel relationship to each other. Indefinite lengths of the untwisted wires 11 and 12 preferably advance continuously at a substantially constant speed determined, for example, by the capstan 16 illustrated in FIG. 2. At the start of the operation, as indicated in FIG. 3-A, the advancing wires 11 and 12 are gripped against twisting at spaced points therealong. Preferably, the advancing wires 11 and 12 are gripped at three spaced points therealong indicated by the letters B, C and D with the central gripping point D equidistant between the end gripping points B and C.

The gripping points are then advanced with the wires 11 and 12 from the positions illustrated in FIG. 3-A to the positions illustrated in FIG. 3-B, and the wires in the spans extending between the gripping points are intertwisted during the advancement of the gripping points with the wires. It is preferred that the speed of advancement of the gripping points he set equal to the wire speed and that the total distance through which the gripping points advance be set equal to one-half of the distance between the end gripping points B and C.

The twisting step may be accomplished by rotating the central gripping point D about the line of advancement of the wires 10 and 11, as indicated by the curved arrow designated twist in FIG. 3-A, during at least a portion of the time that the gripping points advance with the wires 10 and 11 so as to impart twists of opposite hands to the strand lengths extending between the central gripping point D and the end gripping points B and C on either side thereof, as indicated in FIG. 3-B. The duration of twisting rotation of the central gripping point D is limited to either all or some predetermined part of the forward stroke, and the speed of rotation is regulated so as to impart a predetermined length of twist to the twisted pair 10 now extending on either side of the central gripping point D.

If the central gripping point D is rotated in a counterclockwise direction, as viewed from the right of FIG. 3-A and as indicated by the arrow designated twist, then a right-hand twist is imparted to the forward span BD and a left-hand twist is imparted to the trailing span C--D, as seen in FIG. 3-B which depicts the twisting operation at the end of the forward stroke. At or before the end of the forward stroke, the rotation of the central gripping point D is discontinued or the twisting is otherwise stopped, such as by ungripping the wire at the point D.

The gripping points are then released, as indicated in FIG. 3-C, to allow the span BC just twisted to pass to a subsequent apparatus such as the strander 19 illustrated in FIG. 2. Subsequently, the untwisted span of the advancing wires following the now-twisted span B-C is gripped in a similar manner, as indicated by the letters 13', C and D in FIG. 3C, and the operation is repeated.

It should be noted that during the time interval between FIGS. 3B and 3-C, which may be set equal to the time interval between FIGS. 3-A and 3-B, the first twisted section B-C has moved a further distance to the left equal to half the distance between the end gripping points B and C and, in the next twisting operation, the forward end gripping point B corresponds to the trailing gripping point C of the first operation. This is required where a continuous succession of alternating twists are desired; however, if it should be desired to leave an untwisted span between each alternating span of twists, then the second gripping operation is designed to take place after a predetermined untwisted length of the wires 11 and 12 has passed.

Simply, the process may be performed by providing three spaced, aligned gripping members, the central one being rotatable, for holding the wires 19 and 11 against twisting and then moving the gripping members alternately with and against the advancing wires 11 and 12 according to the methods outlined hereinabove.

Referring now to FIGS. 4 and 5, illustrating one particular twisting unit 18 for practicing the foregoing methods, the closely spaced, parallel untwisted wires 11 and 12 advance continuously from right to left, as viewed in FIG. 4, as from the extruders 1717 illustrated in FIG. 2. The advancing wires 11 and 12 pass in succession around the peripheries of three spaced grooved pulleys 23, 24 and 26, which operate to twist the wires 11 and 12 into a twisted pair 10. From the forward end pulley 26, the twisted pair 10 advances to a guide sheave 27, which directs the twisted pair 16 to a subsequent device, such as the strander 19 illustrated in FIG. 2 or r 54 of the switch 52.

4 to a take-up reel in a situation where twisting is the final operation.

The pulleys 23, 24 and 26 constitute means for gripping the advancing wires 11 and 12 against twisting at three spaced points therealong, the gripping points B, C and D occurring at the pulleys 26, 23 and 24, respectively, corresponding to the gripping points depicted in FIG. 3. Each of the end pulleys 23 and 26 is journalled for rotation about its own axis between a pair of opposing arms 28-28 of a supporting bracket, designated generally by the numeral 29. The brackets 29-29 are secured to the upper surface of a carriage 31, which is reciprocable to the left and right, as viewed in FIG. 4, along the line of advancement of the wires 11 and 12.

The central or twisting pulley 24 is journalled for rotation on its own axis between an opposed pair of in clined supporting arms 3232, which in turn are sectu'ed near their lower ends to a rotatable sleeve 33, through which the wires 11 arid 12 advance to the pulley 24. The sleeve 33 is journailed for rotation in a bearing bracket 34, which in turn is secured to the upper surface of the carriage 31. The heights of the brackets 29-29 and 34 are set so that the peripheries of the pulleys 23, 24 and 26 extend along a common line, which becomes the line of advancement of the wires 11 and 12.

The sleeve 33 is rotated at appropriate intervals by means of an electric motor 36 to rotate the central pulley 24 about the line of advancement of the Wires 11 and 12 to intertwist the wires. For this purpose, the motor 36 may be connected through the clutch (not shown) of an electromagnetic clutch-brake unit, designated generally by the numeral 37, to rotate a first bevel gear 38, which meshes with a second bevel gear 39 secured to a reduced end portion 4t) of the sleeve 33. The bevel gear 39 is formed with a central bore permitting advancement of the wires 11 and 12 therethrough to the twisting pulley 24. The motor 36 is mounted on the carriage 31 for movement therewith and a movable power-supply cord 41 is provided for energizing the motor 36. The supply cord 41 is wound around a reel 42, which is biased so that the cord 41 is normally wound thereon, but so that the cord 41 may be withdrawn therefrom as the carriage 31 moves from right to left as viewed in FIG. 4.

The carriage 31 is reciprocated by means of a reversible motor 43 through a gear box 44, a pinion 46 driven from the gear box 4-4, and a rack 47 secured to the under surface of the carriage 31 and meshing with the pinion 46. As best seen in FIG. 5, the carriage 31 is supported for reciprocating movement along a pair of guide rails 48- 48, which are mounted at either end on a pair of upstanding support members 4949. An actuator bar 51 is secured to the upper surface of the carriage 31 and is designed for alternately actuating a pair of limit switches, designated generally by the numerals 52 and 53 (FIG. 4), as the carriage 31 nears the end of the return and forward strokes, respectively.

Control Circuit and Operation Referring now to FIG. 6, showing a control circuit for operating the apparatus illustrated in FIGS. 4 and 5 according to the invention, the limit switch 52 is provided with a lower contact 54 and an upper contact 56 and is biased so that the lower contact 54 is closed at all times except when the switch 52 is positively operated by the actuator 51 at the end of the return stroke. At the end of the return stroke, the upper contact 55 is momentarily closed in order to energize a first control relay 57 across a pair of supply conductors 53-55. When the relay 57 is so energized, a normally-open holding contact 59 thereof is closed in order to maintain the energization circuit therefor through the now-closed contact 59 and a lower, normally-closed contact 61 of the limit switch 53, the contact 61 being similar in operation to the lower contact In this manner, the relay 57 is maintained energized even though the upper contact 56 of the switch 52 is reopened as the carriage 31 begins the forward stroke.

Upon energization of the relay 57, a second normallyopen contact 62 thereof is closed in order to energize a clutch solenoid 63 of the electromagnetic clutch-brake unit 37, thus connecting the motor 36 operatively to the bevel gear 38 (FIG. 4). The motor 36 then begins rotating the twisting pulley 24 about the line of advancement of the wires 11 and 12 so as to begin twisting of the strand lengths extending between the twisting pulley 24 and the end pulleys 23 and 26 on either side thereof. The motor 36 may be energized from a suitable D.C. source 64 through a rheostat 66, which is set to control the speed thereof to impart a desired length of twist to the wires 11 and 1 2 during the forward stroke of the carriage 31.

When the relay 57 is energized, a third normally-open contact 67 thereof is also closed in order to apply power to the reversible motor 43 from a suitable D.C. source 68 across a first pair of supply conductors 69 and '71 through a speed-controlling rheostat 72. Energization of the reversible motor 43 across the conductors 69 and 71 operates to rotate the pinion gear 46 in a counterclockwise direction, as viewed in FIG. 4, in order to cause forward travel of the carriage 31, from right to left as viewed in FIG. 4. The rheostat 72 is adjusted either manually or by any suitable automatic control means (not shown) in order to move the carriage 31 forward at substantially the same speed as the untwisted wires 11 and 1 2 are advancing.

As the carriage 31 reaches the end of the forward stroke, the actuator 51 engages the forward limit switch 53 in order to open the normally-closed lower contact 61 thereof and close momentarily a normally-open, upper contact 73 thereof. When the lower contact 61 is opened, the holding circuit for the first control relay 57 is broken and the relay 57 is de-energized so that the contacts 59, 62 and 67 thereof are reopened. The opening of the holding contact 59 precludes re-energization of the relay 57 when the switch contact 61 recloses. The opening of the contact 62 de-energizes the clutch solenoid 63 in order to disengage the driving connection between the motor 36 and the bevel gear 38, and the opening of the contact 67 disconnects the reversible motor 43 from energization across the first pair of supply conductors 69 and 71.

As the upper contact 73 of the switch 53 is momentarily closed, a second control relay 74 is energized across the supply conductors 58- 58. As the relay 74 is energized, a normally-open holding contact 76 thereof is closed in order to maintain the energization circuit for the relay 74 through the normally-closed, lower contact 54 of the limit switch 52 and the now-closed holding con tact 76 of the relay 74. Thus, the relay 74 remains energized even though the upper contact 73 of the limit switch 53 reopens as the carriage 31 begins its return stroke.

The relay 74 also closes a second normally-open contact '77 thereof in order to energize a brake solenoid 78 of the electromagnetic clutch-brake unit 37. The brake unit positively stops the rotation of the twisting pulley 24 about the line of advancement of the wires 11 and 12 so that no twist will be imparted to the wires during the return stroke of the carriage 31. The relay 74 also closes a third normally-open contact 79 thereof, which energizes the reversible motor 43 across a third supply conductor 81 (alternative to the conductor 69) and the conductor 71, through a speed-controlling rheostat 82.

When the motor 43 is energized across the alternative lines 71 and 81, the pinion 46 is driven in a clockwise direction, as viewed in FIG. 4, in order to move the carriage 31 from left to right to return the twisting pulley 24 and the end pulleys 23 and 26 back to their original positions, as shown in FIG. 4. Since the twisting pulley 24 does not rotate about the line of advancement of the wires 11 and 12 during the return stroke, the twisting unit 18 is passive at this time, the newly twisted pair 10 advancing from right to left and the pulleys 23, 24 and 26 moving from left to right out of engagement with the twisted pair 10. During the return stroke, the pulleys 23, 24 and 26 rotate on their own axes to permit the passage of the twisted pair 10 therepast.

When the return stroke is completed, the actuator 51 again operates the limit switch 52 opening the lower contact 54 thereof and momentarily closing the upper contact 56 thereof in order to initiate the next succeeding cycle of operation as described hereinbefore. As the lower contact 54 is opened, the holding circuit for the second control relay 74 is broken and that relay is de-energized to reopen the contacts 76, 77 and 79 thereof. The opening of the holding contact 76 precludes re-energization of the relay 74 when the switch contact 54 recloses. The opening of the contact 77 de-energizes the brake solenoid 78 to permit twisting rotation of the pulley 24 when the clutch solenoid 63 is re-energized. The opening of the contact 79 disconnects the reversible motor 43 from energization across the alternate supply conductors 71 and 81 permitting re-energization across the conductors 69 and 71 to move the carriage 31 forward.

The setting on the rheostat 82 is adjusted either manually or by any suitable automatic control means (not shown) to regulate the return speed of the carriage 31. It is preferred to regulate the return speed so that when the pulleys 23, 24 and 26 have been returned to their original positions, they engage the span of untwisted wires 11 and 12 immediately following the span just twisted, as illustrated in FIG. 4, so that a substantially continuous alternating succession of twists are formed, without an appreciable length of untwisted wires between the alternating twisted sections.

Alternative Embodiment Referring now to FIG. 7, alternative means are shown for gripping the advancing wires 11 and 12 and for twisting the gripped wires together into a twisted pair 10. The alternative embodiment of the invention includes three opposed pairs of nip rollers 83-83, 84-84 and 86-86. The individual rollers of each pair are biased together to engage the advancing wires 11 and 12, and the pairs are mounted in alignment so that the wires 11 and 12 may advance in a straight line therebetween. The end pairs of nip rollers Sit- 63 and 8686 may be journalled for rotation about their own axes between opposed arms 28'-28' of a pair of support brackets 2929' mounted on a carriage (not shown) similar to the carriage 31 shown in FIGS. 4 and 5.

The central or twisting pair of nip rollers 8484 are journalled for rotation about their own axes between an opposed pair of support members S7-87, only one of which is shown, which in turn are secured to a rotatable sleeve 33' similar to the sleeve 33 shown in FIGS. 4 and 5. A bearing bracket 34' and bevel gears 38' and 39' are provided similar to the members 34, 38 and 39 described hereinbefore, and the remainder of the structure may be the same as illustrated in FIGS. 4, 5 and 6. In operation, the central pair of nip rollers 8484 are rotated about the line of advancement of the wires 11 and 12 during the forward stroke to intertwist the wires, while on the return stroke the twisting is stopped and all of the nip rollers rotate on their own axes to permit the newly twisted pair to pass out of engagement therewith.

Although the illustrated forms of gripping members are preferred, other gripping members might be employed, the prime requisite being the ability to hold the advancing strands against twisting during the forward stroke, yet to permit the twisted strands to pass out of engagement therewith during the return stroke. For example, the gripping members might comprise an opposed pair of jaw members biased to closed positions during the forward stroke and carnmed to open positions during the aesaova return stroke. The central pair of jaw members would then be rotated during the forward stroke to intertwist the strands. One form of twisting member having opposed jaws for twisting, yet between which the strands may advance, is illustrated in Gillis et al. Patent 2,799,299.

The foregoing discussion has related particularly to the twisting of a pair of polyethylene-insulated copper wires, which by nature are sufficiently nonresilient that the alternating twists imparted according to the invention will not subsequently be cancelled; however, in the event that it is desired to twist more resilient strands having any substantial tendency toward cancellation of the alternating twists, a taping or binding head could be provided to apply tape or binding threads to the twisted strands.

While the foregoing methods contemplate that the twisting member should be rotated in the same direction during each forward stroke so that the lengths of the oppositely twisted spans are approximately equal to the distances B-D" and CD in MG. 3, it would also be possible to rotate the twisting member in one direction during one forward stroke and in the opposite direction during the next forward stroke. In this instance, the length of the oppositely twisted spans would be approximately double that shown in FIG. 3. This last method would probably be preferable where relatively long spans are desired between each reversal of twist.

It will be obvious that this invention is not limited to the specific details described in connection with the above embodiments of the invention, but that various modifications may be made without departing from the spirit and scope thereof.

What is claimed is:

1. Apparatus for imparting an alternating succession of twists to a plurality of advancing parallel strands, which comprises a reciprocating carriage, three strandgripping means mounted on said carriage in aligned relationship to each other and designed for gripping the advancing strands against twisting at three spaced points therealong, means for reciprocating said carriage so that said gripping means alternately advance with and return against the advancing strands, means for rotating the central gripping means about the line of advancement of the strands during at least a portion of the time that said gripping means advance with the strands so as to impart twists of opposite hands to the strand lengths extending between the central gripping means and the end gripping means on either side thereof, means for actuating the carriage reciprocating means when the carriage has travelled a distance equal to a desired fraction of a span between the end-gripping means to cause return of the carriage and the gripping means while the strands advance a corresponding distance so that when the gripping means have been return to their original positions they engage a span of untwisted wires immediately following the span just twisted, and means for stopping the twisting rotation of the central gripping means during the time that said gripping means return against the direction of advancement of the strands to allow the twisted portion of the strands to pass out of engagement with said gripping means.

2. The apparatus defined in claim 1, wherein each of the three strand-gripping means comprises at least one pulley, the three pulleys being mounted on the carriage in spaced relationship to each other with their peripheries in alignment so that the advancing strands pass in succession around the peripheries of the pulleys, the central of the pulleys being mounted rotatably about the line of advancement of the strands, each of the three pulleys being also mounted rotatably about the central axis thereof to facilitate the passage of the twisted portion of the strands out of engagement with the pulleys.

3. The apparatus defined in claim 1, wherein each of the three strand-gripping means comprises a pair of nip rollers, the three pairs of nip rollers being mounted on the carriage in spaced relationship to each other and aligned so that the advancing strands may pass in a straight line between the rollers of each successive pair of nip rollers, the central pair of nip rollers being mounted revolvably about the line of advancement of the strands, the rollers of each of the three pairs of nip rollers being also mounted rotatably about the central axes thereof to facilitate the passage of the twisted portion of the strands between and out of engagement with the successive pairs of nip rollers.

4. Apparatus for imparting an alternating succession of twists to a pair of advancing parallel wires, which comprises a reciprocating carriage, three wire-gripping members mounted on said carriage in aligned relationship to each other and designed for gripping the advancing wires against twisting at three spaced points therealong, a reversible motor for reciprocating said carriage in a succession of forward and return strokes wherein said gripping members alternately advance with and return against the advancing wires, a second motor for rotating the central gripping member about the line of advancement of the wires so as to impart twists of opposite hands to the wire lengths extending between the central gripping member and the end gripping members on either side thereof, a clutch for engaging said second motor with the central gripping member, a brake for stopping the rotation of the central gripping member, first switching means actuated by said carriage near the end of a return stroke for disengaging said brake, for engaging said clutch to twist a span of the wires, and for connecting said reversible motor to initiate a forward stroke of said carriage, and second switching means actuated by said carriage near the end of the forward stroke for disengaging said clutch, for engaging said brake to stop the twisting operation, and for reversing the connection of said reversible motor to initiate the return stroke of said carriage thus permitting the twisted portion of the wires to pass out of engagement with said gripping members.

5. Apparatus for imparting an alternating succession of twists to a pair of advancing parallel wires, which comprises a reciprocating carriage, three wire-gripping members mounted on said carriage in aligned relationship to each other and designed for gripping the advancing wires against twisting at each of three spaced points therealong, the central gripping member being equidistant between the two end gripping members, means for moving said carriage forward so that said gripping members travel in the direction of advancement of the wires at substantially the same speed that the wires are advancing, means for rotating the central gripping member about the line of advancement of the wires during at least a portion of the time that said gripping members advance with the wires so as to impart twists of opposite hands to the wire lengths extending between the central gripping member and the end gripping members on either side thereof, means for returning the carriage to its original position, means for operating said carriage-returning means when said carriage has travelled forward a distance substantially equal to one-half of the distance between the end gripping members, means for stopping the twisting rotation of the central gripping member during the return movement of said carriage to allow the twisted wire span to pass out of engagement with said gripping members, and means for controlling the return speed so that when said gripping members have been returned to their original positions they engage the span of untwisted wires immediately following the span just twisted.

6. Apparatus for imparting an alternating succession of twists to a pair of advancing parallel wires, which comprises a reciprocating carriage, three wire-gripping members mounted on said carriage in aligned relationship to each other and designed for gripping the advancing wires against twisting at three spaced points therealong, the central gripping member being equidistant between the two end gripping members, a reversible motor for reciprocating said carriage in a succession of forward and return strokes wherein said gripping members alternately advance with and return against the advancing wires, means for regulating said reversible motor so that the forward speed of said carriage is substantially the same as the speed at which the wires are advancing, a second motor for rotating the central gripping member about the line of advancement of the wires so as to impart twists of opposite hands to the wire lengths extending between the central gripping member and the end gripping members on either side thereof, means for regulating the speed of said second motor to impart a predetermined twist length, a clutch for engaging said second motor with the central gripping member, a brake for stopping the rotation of the central gripping member, first switching means actuated by said carriage near the end of a return stroke for disengaging said brake, for engaging said' clutch to twist a span of the wires, and for connecting said reversible motor to initiate a forward stroke of said carriage, second switching means actuated by said carriage when said carriage has travelled forward a distance substantially equal to one-half of the distance between the end gripping members for disengaging said clutch, for engaging said brake to stop the twisting operation, and for reversing the connection of said reversible motor to initiate the return stroke of said carriage thus permitting the twisted wire span to pass out of engagement with said gripping members, and means for regulating said reversible motor so that the return speed of said carriage is such that when said gripping members have been returned to their original positions they engage the span of untwisted wires immediately following the span just twisted.

References Cited in the file of this patent UNITED STATES PATENTS 2,296,918 Gibson Sept. 29, 1942 2,331,648 Berggren et al Oct. 12, 1943 2,790,299 Gillis et al. Apr. 30, 1957 2,869,316 Lilly Jan. 20, 1959 FOREIGN PATENTS 355,447 Great Britain Aug. 27, 1931 

